Mechanistic study of Eu single atoms occupying four vacancy centers as potential electrocatalysts for the oxygen reduction reaction

Abstract

The oxygen reduction reaction (ORR) on the oxygen electrode plays a critical role in rechargeable metal–air batteries, and the development of electrochemical energy storage and conversion technologies for the ORR is of great significance. In this study, the catalytic performance of rare earth-doped graphene (EuN_xC_6−x-Gra) as an electrocatalyst for the ORR was investigated. The results showed that a majority of the catalysts exhibited good ORR catalytic activity under acidic conditions, with some approaching or even surpassing commercial Pt-based catalysts (η^ORR = 0.45 V). Particularly, EuN₂C₄-2-Gra demonstrated an η^ORR of 0.38 V. It has been observed that the f-band center of Eu atoms increases with an increasing number of N atoms, and the charge distribution exhibits a “U” shape. There is a decreasing trend from N₀ to N₃ and an increasing trend from N₄ to N₆. By incorporating the proportional relationship of the adsorption free energies of reaction intermediates (ΔG_*ads), a volcano diagram was constructed to rapidly assess catalytic activity. Finally, an intrinsic characteristic descriptor φ was formulated to quantitatively describe the relationship between φ and η^ORR, providing a new tool for predicting and designing catalysts. This will provide guidance for the development and design of high-performance rare earth single atom catalysts.